1. Technical Field
The present invention relates to the field of outlet nozzles for use in liquid fuel rocket engines. Also, the invention relates to a method for manufacturing these nozzles. The invention is especially intended for use with respect to cooled outlet nozzles for rocket motors driven by liquid fuel.
2. Background of the Invention
During operation, a rocket nozzle is subjected to very high stresses, for example in the form of a very high temperature on its inside (on the order of magnitude of 980° F.) and a very low temperature on its outside (on the order of magnitude of 370° F.). As a result of this high thermal load, stringent requirements are placed upon the choice of material, design and manufacture of the outlet nozzle. At a minimum, the need for effective cooling of the outlet nozzle must be considered.
Cooling is provided by attaching individual lengths of tubing on the inside surface of the nozzle. The geometry of each tube is such that it must conform to the conical or parabolic shape of the nozzle. Additionally, the entire inside surface of the nozzle must be covered to prevent “hot spots” which could result in premature failure of the nozzle. Each nozzle typically has a diameter ratio from the aft or large outlet end of the nozzle relative to the forward or small inlet end of the nozzle ranging from 2:1 to 3:1.
According to a previously known method of manufacturing a cooled outlet nozzle, rectangular tubes of constant cross section made from nickel-based steel or stainless steel are utilized and arranged parallel with another, and are welded together.
The tubes are helically wound such that they form an angle of helix in relation to the longitudinal axis of the nozzle, which angle increases progressively from the inlet end of the nozzle to its outlet, thereby forming a bell shaped nozzle wall. Rocket engine exhaust flowing along the inside surface of such a nozzle with helically arranged tubes results in an angled reaction force that endures a roll momentum on the rocket and which must be compensated for by some additional means. These additional means often lead to increased weight and increased flow resistance. Having long channels without any increase in cross section will also affect the coolant flow resistance negatively.